東沙衛星追蹤站穩定度分析

Abstract

東沙島位於東沙環礁，由珊瑚沙堆疊而成。由於珊瑚沙膠著程度低，故其上建築物有沉陷傾斜之可能。東沙衛星追蹤站為TWD97基準之框架點位之一，故該點位之穩定性具有深入探討確認之重要性。 本研究使用1995至2012年十八年接收頻率30秒之GPS觀測數據，於每年選定一天進行精密單點定位計算後，組成座標時間序列，分析該點之變化特質。而東沙地區氣候可分為西南季風與東北季風兩個季節，前者由五月至十月，後者由十一月至四月，為了解不同季節之差異，選取近三年二月及八月之第一個星期，進行逐筆精密單點定位計算衛星追蹤站之座標並分析其點位變化，此觀測數據亦為30秒觀測數據。本研究使用GPS網路自動化算系統CSRS-PPP和APPS以及GPS數據後處理軟體GrafNav進行精密單點定位解算，並對於各測站座標變化進行分析。 由逐年選定一天計算之分析成果中顯示，墾丁衛星追蹤站座標點位變化趨勢呈現往西移動，移動量約為30公分，陽明山、北港及東沙衛星追蹤站平面座標呈現朝東南方移動之變化趨勢，陽明山衛星追蹤站移動量往東約為60公分，往南約為24公分，北港衛星追蹤站移動量為往東約60公分，往南約15公分，東沙衛星追蹤站移動量往東約為55公分，往南約為20公分。陽明山、墾丁及東沙追蹤站在垂直方向無明顯趨勢變化，北港衛星追蹤站高程下降約為42公分。由近三年2月及8月第一個星期之成果分析中顯示，衛星追蹤站之點位變化趨勢與季節氣流較無相關。

Dongsha Island is a part of Dongsha Atoll. The top soil is mainly decomposed coral reef. Because the cementation level of this type soil is low, the construction on top may suffer subsidence problem. Dongsha satellite tracking station established by MOI is one of the eight framework stations for TWD97. The importance is high. This study investigates the stability of Dongsha satellite tracking station. GPS data collected during 1995 to 2012 at 30 second interval is used for analysis. Precise Point Positioning (PPP) schemes, namely, CSRS-PPP, APPS and GrafNav, are applied for deriving the three dimensional coordinates for study. The first analysis takes one day in each year and comparing the daily solution. The second analysis takes the first week of February and August in 2009, 2010, and 2011. The weather of Dongsha area can be classified into the South-west wind and North-east wind seasons. The first season is generally from May to October, and November to April for the second. From the first analysis, the horizontal coordinates of KDNM is about 30 cm westward. The (E,N) coordinates change of YMSM, PKGM, and TNSM are (-24 cm, 60 cm), (-15cm, 60cm), (-20cm, 55cm) respectively. There is no significant trend of elevation change for KDNM, YMSM, and TNSM tracking station. But, the height of PKGM decreased 42 cm. For the second analysis, no significant relation between the coordinate change and the seasons is observed.